Apparatus for exciting alternators



Se t. 23 1924.

p A. BLONDEL APPARATUS FOR EXCITING AI'JTFIRNA'IORS Filed Feb. 28. 19203 Sheets-Sheet 1 Fig. 4

villi/Ill 0 A. BLONDEL.

APPARATUS FOR EXCITING ALTERNATORS Sept. 23 1924- Filed Feb. 28 1920 3Sheets-Shoot wwM 2 7 4 Sept. 23, 1924. 1,509,501

A. BLONDEL APPARATUS FOR .lXCITliyG ALTERNATORS Filed Feb. 28. 1920 3Sheets-Sheet 5 A rra/m i-rsl Patented Sept. 23, 1924.

UNITED STATES ANDRE BLONDEL, OF PARIS, FRANCE.

APPARATUS FOR EXCITING ALTERNATORS.

Application filed February 28, 1920. Serial No. 361,978.

To all whom it may concern:

Be it known that I, Arman BLONDEL, of 41 Avenue de La Bourdonnais,Paris, France, engineer, have invented new and useful-Improvements inApparatus for Exciting Alternators, which apparatus is fully set forthin the following specification.

This invention relates to means for exciting alternators which workeither as generators or receivers (synchronous motors) the object beingto reduce the amplitude of the oscillations to which they are subjectedif coupled and the miximum current which they first deliver whenaccidentally shortcircuited.

It is known that the armature reaction of alternating current generatorsproduces a lowering of voltage at the brushes, when the machine works,this voltage drop being due to the wattless current-component.

Many authors. amongst which can be cited Rice, Blondel, Boucherot, LeBlane, Danielson, Lunt, Iiatour, Johnston, Siemens & Halske, havepreviously proposed excitation-methods by which this effect may beannulled, by a compensation of the armature reaction obtained bydifferent ways, and

particularly by the use, as exciter, of a rotating converter, fed by acurrent furnished by transformers mounted in series or in shunt. Thisexcitation means is well known, but the compensation of the armaturereaction is objectionable for it increases the current intensity when ashort circuit takes place; and increases the reactions of the coupledalternators.

I have discovered that in order to facilitate the parallel running oftwo or more alternators, for the feeding of a net, these alternatorsbeing actuated by reciprocating engines, it is advisable to reinforce asmuch as possible the armature reaction by the effect of the wattlesscurrent which run between machines.

My process is intended to be applied to alternators, the voltage ofwhich is regulated by the variation of resistances inserted in the fieldwindings. This resistance variation may be controlled automatically byknown systems as those of Tirrill, Thury, Brown-Bovery. etc. In carryingout this process it is aimed to aggravate the armature reaction of analternator without detracting from its voltage regulation, and with theaim to reduce the wattless currents exchanged by the transformers whenthey work in parallel, and also to slow down and damp the localoscillations of the alternatorsQ Experience shows that the oscillationsof alternators coupled singly or in parallel to the line and working asgenerators can be reduced by varying the inducing field in accordancewith the variation of the direct reaction flux of the armature throughthe field circuits.

' On the other hand experience has shown that on the suddenshort-circuiting of an alternator the demagnetization of the fieldmagnets under theeifect of the direct reaction of the armature isretarded by the current induced in an unfavorable direction which thisreaction generates in the exciting circuit. This unfavorable effectwould evidently be reduced if at the same moment the variation of thecurrent is made to cause an electromotive force of opposite sign to thatwhich produces the diminution of flux by the induced field of fluxtraversing the primary circuit to act in the exciting circuit.

In both cases it will be seen therefore that it is desirable wheneverthe direct reaction of the armature causes a diminution of the flux ofthe field magnets to bring about an instantaneous diminution of theelectromotive force applied at the terminals of the exciting winding ofthe field magnets, for this will cause a reduction of the current whichnormally passes from the exciter or from the exciter lbars of thecentral station to the field magnets of the alternator.

The present invention consists in the addition to any excitingalternator of an arrangement for exciting which produces suchinstantaneous reduction of the electromotive force proportionally to thevariation of the armature counter-ampere-turns opposed to the fieldmagnets, in combination or otherwise with other processes for automaticrelatively slow regulation of the field excitation which allow thediiference of the potential at the terminals of the alternators or at asuitable point of distribution in the line fed by this alternator to bemaintained constant between appropriate limits.

It will be well to explain here that numerous processes are known forsuch automatic regulation of the tension of an alternator excited by anexciter of ordinary type.

In particular there may be cited the automatic regulators of Thury andof Tirrill as characteristic types of apparatus for obtain I ing theobject desired by difierent means.

Thurys process consists in the automatically actuated-rheostatcontrolled by a simple or compensating voltmeter (compensated bythecurr'ent in such a manner as to take into account the loss of linetension); so soon as the tension of distribution falls below the fixedvalue, the handle of the rheostat comes automatically into action insuch manner as to lessen the resistance of the excitmg circuit ofthealternator until the tension has regained its normal value; therheostat is operated in inverse directlon if the tension rises above thedesired value. v

In the Tirrill process the same result is obtained by means of atrcmbler or of a contact which short-circuits and introduces aresistance mounted in series in the exciting circuit; the ratio of thedurations of closing to the durations of opening being modified toobtain a larger or smaller exciting current. This ratio is alsoconstantly regulated by an electro-magnet placed under the control ofthe tension of distribution.

These regulating apparatus or any other analogous apparatus may beinterpolated, for example, in one of the exciting circuits of theexciter which delivers current to the circuit of the field magnets ofthe alternator.

According to the present invention, an exciter of the ordinary type ofalternators 1s modified by providing it with a counter-compoundingarrangement, that is to say an arrangement which produces the inverseeffect to that which is instantaneously produced in compound exciters bythe action of the current delivered by the alternator. The most simplemethod of obtaining this result in the general case of a polyphasealternator having any desired number of phases, consists, for instance,in interpolating in each of the conductors passing from the alternator,the primary of a series-transformer analogous to those employed forcompounding alternators and in causing the secondary circuits of each ofthese transformers to act in the opposite direction to that which wouldbe required to produce the compounding (that is regulation of thetension).

In the accompanying drawing:

Figs. 1 to 5 illustrate diagrammatically some methods of carrying outthe invention.

Fig. 6 shows the rheostats of a Thury regulator.

A is the armature of the alternator (for the sake of clearness, it issupposed to be a monophase alternator); M is the inducing circuit; f, f,are wires leading from the alternator and corresponding to one of thephases; B, B are the alternating current us bars of the central stationgenerator or a portion of the central station; f, f, are

wires leading to a second alternator coupled in parallel with thealternator A; B B are collectin bars located at some other point fromWhlCh pass the feeders at the outlet of verter (or the dynamo in Fig.4), of a suitable type; J, J its field magnet; 12, b, b, b, are therings of the ordinary winding of the armature or of a windingsuperimposed on the same armature of the rotary converter E,; E is arotary-converter or a dynamo; J J, are its field magnets; 5 b the ringsofthe converter E alternating current side; C, C are a pair of twodirection contacts; N is a battery of accumulators.

D is a counter-compounding series transformer: D a transformer connectedin parallel with the wires f, f, of the alternator or with a group B,13,; D. is an exciting transformer whose primary is in series with theexciting circuit of the alternator and whose secondary feeds a specialcircuit placed on the field magnets on the exciter E, (or of the exciterE in Fig. 3); R, R R R are exciting rheostats; S is a reactor, T, T areautomatic excitation regulators: of course only one of these automaticregulators is provided for each alternator or for each group ofalternators working in parallel ;'the diagram shows two examples of thearrangement. K, K are switches which serve to cut out the unusedregulator; P is a tension limiting arrangement or discharger of a knowntype seen in Fig. 3 only, but which may be introduced in any otherarrangement. I is a circuit breaking switch controlled by windings m, orm, and by the transformer D; it breaks the exciting circuit in the caseof an undue output from the alternator: it may be provided in any of thearrangements.

Fig. 1 shows an arrangement which may be adopted when each alternator ata generating station is provided with a countercompounding exciter fedon the alternating current side with current resulting from twotransformers, series and parallel.

Fig. 2 shows the employment of a similar counter-compounding rotaryconverter but having two alternative windings fed respectively from twoseparate circuits, one derived from a series transformer, the other froma transformer fed in derivation.

Fig. 3 corresponds to the case in which the counter-compound exciterwhose armature receives alternating current from a countercompoundingtransformer is itself excited of bus bars B, B or. v

partly in shunt (or in series) partly from an independent excitationwhich may be derived from a battery of accumulators, a dynamo or arotary converter.

F r instance, the compounding effect is pr need by a dynamo E of anytype whose armature is in the excitin circuit of the alternator andwhose field is fed from any source as for example from dynamo E Thisdynamo E is thus excited from an in dependent circuit and the rings b 6of its armature are connected to the transformer in series with thecircuit of the alternator in such a manner as to produce a magneticeflect opposite to the field produced by the independent excitercircuit.

Figs. 4 and 5 showspecial exciting windings which augment the apparentself-induction of the field circuits and which may respectively beadapted to the arrangement shown in Figs. 1, 2 and 3.

In all these figures, the circuit of the alternator is supposed to bemonophase for the sake of clearness, but usually the alternator will beprovided with any desired number of phases and poles. In the same way,the counter-compound transformer may have any number of phases and feeda corresponding number of phases of any of the rotary converters shown.

When the transformer D is common to several alternators working inparallel, its secondary is connected to the exciting bars B, B fromwhich the Wires which feed respectively each of the exciters E on thealternating side lead to the rings 6 b in the case of Fig. 1, to therings 6 b in the case of Fig. 2, and to the rings 6 b (Fi 3) for arotary converter E of any type wliich may be provided for the purpose ofproducing a continuous independent excitation of the exciter E Thereexist three main types of known arrangements of compounding converters;a first which utilizes for its alternate cur rent feeding of thearmature the tension derived from the transformer D and from thetransformer D (Fig. 1). The compounding windings may be distinct fromthe winding which delivers continuous current (Leblanc type forexample). A second which receives in two separate windings on thearmature, currents produced respectively by the two electromotivecomponents of the transformers D. and D Fig. 2. A third which onlyutilizes on the alternating side-current produced by the tension of theseries transformer (Fig. 3).

According to this invention one or other of these arrangements ismodified by inverting the direction of the connections of the secondaryof the series transformer with respect to the rings 6, 6 The degree ofcounter-compounding may be regulated varying the electromotive forceproduced in the secondary of the series transformer; this may beeffected by varying the ratio of transformation in any of the well knownwags.

f course, all phases should be regulated in the same manner; one phaseonly ,is shown in order to simplify the figures.

The position of the armature of the exciter or rotary converter E on theshaft of the alternator with which it is fast is regulated in such amanner that the field produced' by the compounding currents (that is tosay by the currents which are in phase opposite to those of theprimaries of the series transformer) is in direct opposition with thenormal inducing field of the exciter; this therefore acts ascounter-compounding.

The continuous excitation of the exciter E may be effected in series orin shunt (but preferably in shunt in the arrangements shown in Figs. 1,2 and 3) by the circuit passing from the brushes of the commutator.

The exciter may be stabilized by providing it with a continuoussupplementary excitation through an independent circuit. Thisindependent excitation may be derived for example from an exciter Earranged in each alternator; but usually it would be common to a portionor to the assemblage of the station alternators working in parallel.

This allows the exciter E to be actuated by a shaft independent of thatof the alternator; it may be driven by an asynchronous or synchronousmotor or may itself be a rotary converter receiving alternating currentderived from a transformer in shunt as shown in Figs. 3 and 4: in thislatter case only it is provided with rings 6 and b In all the precedingarrangements there may be provided another partial excitation of theexciter E caused by variable currents generated in the exciting circuitof the field magnets of the alternator during the oscillations of thislatter or when a sudden overcharge (flow of current) occurs. Thisexciting winding is shown diagrammatically in Figs. 5 and 6 in which itis shown alone in order to simplify the diagrams; it may however besuperposed on the other field magnet windings or may replace one ofthem. The exciter thus counter-compounds itself but only for variationin speed of the alternator which it excites because the induced currentshave the frequency of the hunting oscillations of the armature of thealternator about the mean speed. finally this winding produces for itsfrequency the same effect as that of a self-induction interpolated inthe circuit of the field magnets. Of course a resistance is introducedinto this inducing circuit sufficient to enable the current produced tobe'substantially in phase with the electromotive force induced in thesecondary of the transformer D,.. This secondary may feed the excitingcircuit of E in place of E when there is an exclter E the effectproduced remains of the same na ture.

Alternators thus compounded may also advantageously be employed toreduce the effects of shortcircuiting; directly a shortcircuit in theline or in the Wires connecting the alternators to the bars takes place,the counter-compounding series transformer D delivers an intensedemagnetizing current into the armature of the exciter whose tensionwill be reduced. This effect is again increased by the influence of theexcitation in shunt. The exciter will thusaid in the demagnetization ofthe field magnets which tends to cause the armature reaction of thealternator but which is hindered when there is no counter-compoundingand this will take place mainly at the commencement of the short-circuitby the sudden increase of current in the field magnets,-the well knownphenomenon discovered by Dr. Punga.

The presence of a reactor S reduces such afliux of current and favorsthe fall of tension at the brushes of the exciter.

Counter-compounding allows alternators to be more economicallyconstructed as the gap may be reduced and therefore the ampere-turns onits field magnets.

It may be objected that this arrangement increases to a greater or lessextent the variations in voltage in function of the load above all whenthe current produced by the alternator is wattless. Inorder tocompensate for this increase of variation there may be added to thearrangement a tension regulator of one of the lfiiown types (see whathas been stated above) this regulator has its main circuit interpolatedin series either in the excitation circuit of the exciter E1, or in theexcitation circuit of the exciter 133 In both cases, the effect of the,automatic regulater is progressively to modify the tension at theterminals of the field magnets of the alternator in such a manner as tore-establish the desired tension of distribution in spite of thecontrary effect of the countercompounding exciter. In order to avoid inthe case of a short-circuit the automatic regulator counterbalancingexcessively the effect, of the counter-compounding cxciter, suchautomatic regulator is regulated in such a manner that in norm-a1working it can only deliver to the alternator an exciting current notgreater than that which the largest output requires; there may even beadded to the automatic regulator a working terminal which cuts out itscircuit or which interpolates in its circuit a very large supplementaryresistance as shown at B in Figs. 4 and 5 in which the rheostat of aThury regulator is shown diagrammatically so that after having increasedthe excitation to a very high value the automatic regulator continuingits action suddenly reduces the excitation to a mimmumvalue.

When these automatic regulators are 'placed in the position T Figs. 1 to3, it may also be desirable that they should have a sufliciently slowaction orevenbe retarded by some arrangement in order to prevent theiraction from being felt during the duproviding a counter-compoundingaction in such manner that an instantaneous increase of the series wattcurrent exchanged between the alternators causes an instantaneousdiminution of the field current and automatic slow-acting means forcompensating for disturbance of the busbar voltage attendant upon theaction of the devices responsive to current exchanged between thealternators.

2. Means for controlling the amplitude and frequency of oscillations dueto hunting ofa system of alternators feeding busbars in parallel,comprising a series trans- I former inserted in the mains of thealternator, a commutator machine connected to the secondary circuit ofthe series transformer, said commutator machine feeding the field coilsof the alternator or alternators and providing a counter-compoundingaction in such manner that an instantaneous increase of the series wattcurrent exchanged between the alternators causes a diminution of thefield current, combined with means for'regulating the transformationratio of the series transformer, and with an automatic slow-acting fieldcontrol device for restoring at the busbars the proper regulation of thedistribution voltage.

'transforming our i comprising a separate field magnet winding placed onthe field magnets of the exciter and means at the generator station forsupplying an independent exciting current to such windin 4. Means ircontrolling the amplitude of oscillations due to hunting of a system ofalternators feeding busbars in parallel, comprising a series transformerinserted in the mains of the alternator, and a commutator machineconnected to the secondary circuit of the series transformer, saidcommutator machine feeding the field coils of the alternator oralternators and providing a counter-compounding action in such mannerthat an increase of the series current causes a diminution of the fieldcurrent, combined with an automatic voltage regulator for correcting themean value of the variations in voltage independently of the periodicvariation produced by the said oscillations due to hunting.

5. Means for reducing the amplitude and frequency of the freeoscillations of alternators coupled to one another, comprising anexciter for each alternator and means for producing an instantaneousreduction of the electromotive force of said exciter proportionally withthe variations of current exchanged between machines and armaturecounter ampere turns opposed to the field magnets substantially asdescribed.

6. Means for reducing the amplitude and frequency of the freeoscillations to which alternators are subjected when coupled or themaximum current which they first deliver when accidentallyshort-circu'ited, comprising means for transforming current exchangedbetween the machines and means for utilizing the transformed current toproduce an instantaneous reduction in the field excitation of analternator.

7 Means for reducing the hunting action of alternators coupledin'parallel or the maximum current delivered when short-circuited,comprising means for transforming alternating current exchanged betweenthe alternators and means for utilizing the transformed current toproduce a diminution of the exciting current of an alternator.

8. The combination with a system of alternators having fields eachexcited by a current from a rot y converter, means for ant flowing inseries between the alternators and means for utilizing the transformedcurrent to cause diminution of said exciting current in accordance withan increase of said series current thereby controlling the amplitude andfrequency of the free oscillations due to hunting action of the system.

9. The combination with an alternator,

of a compound exciter therefor, means for instantaneously producing adiminution of the electromotive force applied at the terminals of theexciting winding and field magnets by the action of the increasedcurrent delivered by the alternator and means for producing automatic,relatively slow regulation of the field excitation to maintain thedifference of potential constant.

10. The combination with an alternator, of a counter-compounding exciterand a series transformer feeding current to the exciter, said exciteracting on sudden increase of or diminution of series current to cause aninstantaneous diminution or increase of the field current in combinationwith a slowacting controlling device for the field excitation of thealternator producing a slow increase or decrease thereof.

11. The combination with an alternator, of a rotary converter operatedby alternating current and supplying exciting current for the alternatorfield, a transformer in a series connection from saidalternator to themains, a transformer in parallel or connected across the terminals ofthe machine and connections between the secondaries of said transformersand the alternating side of the converter to feed said converter withcurrent compounded from said transformers, and an independently actingautomatic selfexcitation regulator for the field of said converteracting oppositely to said compound ing device.

12. The combination with an alternator, of a rotary converter supplyingexciting current for the field alternator and fed on its alternatingcurrent side with current from transformers, series and parallel, anautomatic self-excitation regulator for the field of said converter anda continuous supplementary excitation through an independent circuit forstabilizing the exciter.

13. The combination with an alternator, of a rotary converter feedingthe field of the alternator, a series transformer inserted in a main ofthe alternator and feeding alternating current to the alternating sideof the rotary converter, said converter supplying diminishing current tothe field of the alternator on increase of series current in thetransformer and means for partially exciting the field of the rotaryconverter by variable currents generated in the field magnet circuit ofthe alternator by oscillations of the alternator or sudden overcharge.

In testimony whereof I have signed this specification.

ANDRE BLONDEL. Witnesses:

Fnnnnaro HARLii, HENRY T. Wmoox.

